What happens to euglena when sunlight is not present?

Euglena is a genus of eukaryotic unicellular flagellates. Species of Euglena have characteristics of both plants and animals. Euglena have photosynthesizing chloroplasts within their cell which enable them to make their own food in sunlight just like plants. When sunlight is not present, euglena becomes distinctly animal-like. Its cells will absorb food (organic substances) from the environment (heterotrophically).

any abiotic or biotic factor in an ecosystem that causes a population's size to slow or decrease is a limiting factor.

"do a testcross with a homozygous recessive plant."